Deuteronomy 15:19

“Sanctify to Me every firstborn, the first offspring of every womb among the sons of Israel, both of man and beast; it belongs to Me.”

“And you shall do the same with your oxen and with your sheep. It shall be with its mother seven days; on the eighth day you shall give it to Me.

“But the firstborn of an ox or the firstborn of a sheep or the firstborn of a goat, you shall not redeem; they are holy. You shall splash their blood on the altar and shall offer up their fat in smoke as an offering by fire, for a soothing aroma to Yahweh.